This section is intended to provide a background to the various embodiments of the technology described in this disclosure. The description in this section may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and/or claims of this disclosure and is not admitted to be prior art by the mere inclusion in this section.
Within the umbrella work of small cell enhancements undertaken by the Third Generation Partnership Project (3GPP), a new transmission scheme known as dual connectivity is being standardized. The dual connectivity is defined from the User equipment (UE)'s perspective, with its name suggesting that the UE communicates with two different RBSs via simultaneous communication connections. The RBSs involved in the dual connectivity may operate on the same frequency or separate frequencies. Each of the RBSs may or may not define a stand-alone cell.
By way of example, FIG. 1 schematically illustrates a common scenario of the dual connectivity, wherein a UE performs two-way communications with two RBSs (e.g., a macro RBS and a pico RBS).
Although many similarities are shared by dual connectivity, carrier aggregation and Coordinated Multi-Point (CoMP), the dual connectivity is less demanding on backhaul delay and synchronization between different network points as compared with the carrier aggregation and the CoMP.
A straightforward implementation for dual connectivity would be having a high-profile UE capable of simultaneously transmitting to and receiving from different RBSs perform dual connectivity with two RBSs. Although less system design effort needs to be made for this implementation, the complexity and thus the cost of the high-profile UE are relatively high. In the scenario where the dual connected RBSs operate on separate frequencies, the complexity of the UE would be further increased because the UE needs to support Uplink (UL) dual frequency carriers. In the scenario where the dual connected RBSs operate on the same frequency, there would be some “dead zones” (e.g., in the vicinity of the pico RBS), where the UE cannot hear from the RBSs simultaneously due to a large difference in dynamic range between two Downlink (DL) signals. Another disadvantage of this implementation is that inter-modulation products may result from superposition of more than one UL signals at each RBS.
For UEs incapable of simultaneously transmitting to and receiving from different RBSs to achieve dual connectivity, a different implementation based on TDM-based resource partition between dual connected RBSs may be applied. Although this implementation becomes more complicated in system design, it allows UEs incapable of simultaneously transmitting to and receiving from different RBSs to achieve dual connectivity and thus significantly reduces the requirements on UE complexity. Moreover, when this implementation is applied, the UE does not need to monitor scheduling grants from the dual connected RBSs and the problem with inter-modulation products does not exist.